APPROACHES FOR STABLE MULTIJUNCTION A-SI SOLAR-CELLS

Improvements in the stabilized efficiency of single-junction and multi -junction amorphous silicon (a-Si) solar cells have been studied. The stabilized efficiency, or efficiency after light exposure, of a-Si sol ar cells can be improved by suppressing impurities such as oxygen and nitrogen in the intrinsic (i-) layer of the cells. It has also been fo und that the defect density of a-Si films and conversion efficiency of a-Si solar cells both at the initial state and the stabilized state a re strongly correlated with the content of hydrogen having an SiH2 con figuration rather than with the total hydrogen content in a-Si i-layer s. This strongly suggests that some measures are still available to re duce the stabilized N-d of the a-Si i-layer while conserving the suita ble optical properties. A practical estimation method, which considers the variation of the I-V characteristics of each component cell, is a lso developed in order to optimize multi-junction cells. Stabilized ef ficiencies of 8.8% for a single-junction a-Si solar cell and 10.6% for an a-Si/a-SiGe double-junction solar cell have been achieved for 1 cm (2) cells.